1. Field of the Invention
The present invention relates to operating fluids for pneumatic and hydraulic devices and inflatable articles such as vehicle tires.
2. Brief Description of the Prior Art
Inflatable vehicle tires are a critical component of transportation in the modern economy. Invented in the United Kingdom in the late 19th Century, inflatable pneumatic tires are conventionally filled with compressed air, although other gases have been used in special circumstances. Similarly, commercial and industrial equipment typically use compressed air as an operating fluid due to its low cost.
Correct inflation is highly significant when considering tire life, safety, and performance. It is not always possible to look at a tire and detect under-inflation. However, under-inflation can cause many tire-related problems. As inflation pressure largely determines a tire's load capacity, under-inflation results in an overloaded tire. An under-inflated tire operates at high deflection resulting in decreased fuel economy, sluggish handling and may result in excessive mechanical flexing and heat build up leading to catastrophic tire failure.
More recently, nitrogen, a dry, inert gas has been used to inflate airplane tires, off-road truck tires, military vehicle tires, and race car tires for improved performance. The rationale for the use of nitrogen is related to the fact that oxygen in compressed air permeates through the wall of the tire, thus reducing the tire's inflation pressure. During this process and its journey through the tire wall, oxygen oxidizes the rubber compounds in the tire, causing under-inflation and deterioration of the rubber. In addition, the deterioration of the rubber further increases the tire and liner permeability, as well as, intracarcass pressure, thus resulting in further damage and under-inflation of the tire. Dry nitrogen can maintain proper inflation pressure and prevent auto-ignition, will not corrode rims, and will help the tire to run cooler. The result is increased safety and reduced operating cost.
Portable tire sealing and inflation devices are well known for emergency use by motorists to temporarily seal and inflate punctured vehicles tires. Typical compositions for use in such devices include a sealant and a pressurized gas to blow the sealant into the punctured tire and to inflate the tire. The pressurized gas can be generated in situ from a suitable compound and an activating material, or prepackaged with the sealant. Examples of gases that have been used or considered for use in tire sealing and other tire inflation devices include various hydrocarbons and chlorofluorocarbons, carbon dioxide, nitrous oxide, nitrogen and air.
However, various disadvantages have been disclosed in respect to many of these gases. For example, use of carbon dioxide, nitrous oxide, nitrogen and air is not practical, because the U.S. Department of Transportation has set a limit of 180 psig at 130 degrees F. for interstate shipping of products in pressurized aerosol cans. Under these conditions many materials that remain gases at room temperature under elevated pressure require too large a volume at the 180 psig pressure limit to be practical.
Even materials that condense under pressure, and thus, in the liquid phase, require much smaller volumes, may have significant disadvantages, such a flammability (hydrocarbons) or ozone-depleting qualities (chlorofluorocarbons with high ozone depletion potentials, such as “Freon 11,” trichlorofluoromethane, and “Freon 12,” dichlorodifluoromethane). Other materials may not be suitable as a tire inflatant for other reasons. For example, U.S. Pat. No. 6,605,654 discloses that 1,1,2,2-tetrafluorethane (HFC-134a) has a very high vapor pressure at 130 degrees F. (199.2 psig) such that vapor pressure depressants such as butyl cellosolve, acetone, methyl ethyl ketone, or acetonitrile must be mixed with 1,1,2,2-tetrfluoroethane when it is employed as a propellant.
Another consideration is the rate of diffusion of the inflatant material in the tire rubber. The greater the rate of diffusion through tire rubber, the faster the loss of the target inflation pressure, the more frequently tires must be reinflated. Compared with air, nitrogen has a lower rate of diffusion in tire rubber, and has been promoted as a desirable substitute. Filling tires with nitrogen can reduce the extent of underinflation. Tire underinflation is associated with shortened tire life, reduced fuel mileage, and poorer road handling.
There is a continuing need to reduce vehicle fuel consumption, reduce tire underinflation, extend tire life, and improve motor vehicle safety.